Increasingly, nitrogen management is becoming an issue for the
wastewater treatment community. Nitrogen concerns mainly fall into
two categories: environmental health, and public health. In regard
to the former, wastewater may contribute to eutrophication of lakes and
streams. (Eutrophication is a condition characterized by high
biological productivity, leading to algae blooms, oxygen depletion, fish
kills, and other disturbances of the surface water ecology.) In
regard to the latter, nitrate contamination of groundwater is often a
concern because of claims linking it to blue-baby syndrome (infant
methemoglobinemia), increased risk of cancer, miscarriage, and diabetes.
Doubt about the validity of those health concerns has been growing, due
to the lack of substantive and reproducible supporting evidence.
Nevertheless, regulations increasingly impose highly restrictive
discharge standards for treated wastewater, often requiring that
treatment systems meet a limit of less than 10 mg/L total nitrogen at
end-of-pipe. The federal drinking water standard for nitrate is
usually cited as the basis for restrictive discharge standards, though
by law that standard applies only to public water supplies, not to
private wells or to discharged waste.

Whether the
concern is environmental health or public health, and regardless of the
validity of public health concerns, it is important that the
decentralized wastewater treatment industry be prepared to meet
stringent discharge standards where required. The industry is
actively responding to this need. But it's important to not that
there is a correlation between cost and level of treatment.
Cost-effective advanced treatment systems are available that - when
properly designed, built, installed, operated, and maintained - reliably
produce effluent with nitrogen concentrations less than 20 mg/L (a level
that represents approximately 69% nitrogen reduction, assuming typical
residential wastewater strength).

A few
manufacturers also provide systems designed to consistently and reliably
meet a more stringent 10 mg/L target (representing further reduction of
only 16%). However, this relatively small gain in nitrogen removal
comes at a disproportionately high cost. Such systems require
supplemental treatment steps and devices that add substantially to
costs. For example, devices to deliver supplemental carbon and/or
alkalinity may be needed; and additional tanks or compartments may be
needed to increase hydraulic residence time and provide anoxic
conditions that favor denitrification. These features require more
intensive operation and maintenance, and regulators may demand more
frequent monitoring and inspections, raising costs even more.

Moreover, it
should be kept in mind that onsite systems are not the only source of
nitrogen inputs to ground or surface waters, nor are they typically the
source that has the greatest impact on water quality. Nitrogen
from agricultural or residential fertilizers, atmospheric decomposition,
and animal feeding operations can be major contributors. For
example, for the Chesapeake Bay area it has been estimated that only
about 4% of nitrogen loading to the Bay derives from septic system
waste, whereas 31% is from agricultural fertilizers; 26% is from
atmospheric decomposition; 20% from municipal and industrial wastewater;
10% from non-agricultural fertilizers; and 8% from animal feeding
operations.* (Anderson, DL, 2006. A Review of Nitrogen
Loading and Treatment Performance Recommendations for Onsite Wastewater
Treatment Systems <OWTS> in the Wekiva Study Area. Figure 6.
February 5, 2007 from
http://member.fhba.com/docs/Septics Final Wekiva Paper 2 14 06.pdf.)

Where
nitrogen loading is a concern, it is critical that all of the
contributors be identified, and that the burden of nitrogen management
be assigned proportionally. Practical, cost-effective management
solutions should be required of all sectors, especially those sectors
contributing the greatest share of the load.